Prunus pumila dwarfing rootstock named `Renus 2`

ABSTRACT

Prunus pumila variety `Rhenus 2` is a dwarfing rootstock that is compatible with Prunus varieties such as peach, nectarine, and apricot, producing dwarf trees with no significant reduction in fruit size, early yield, high yield efficiency, uniform fruit size, high frost hardiness, no suckering, and good soil adaptation.

BACKGROUND OF THE INVENTION

The present invention comprises a new variety of sand cherry, or dwarfcherry (Prunus pumila), referred to by the varietal name `Rhenus 2`.`Rhenus 2` is useful, for example, as a rootstock for peach, nectarine,apricot, and other Prunus varieties, displaying good compatibility andproducing dwarf trees with high yield efficiency and high frosthardiness, thus allowing such varieties to be grown in colder climates.

The new variety was selected by me in a cultivated area in an orchard atthe Research Station of Viticulture and Horticulture in Geisenheim,Germany. At the Research Station, fifty-five Prunus pumila seedlingsresulting from open pollination of a Prunus pumila maternal parent wereselected for testing. Five peach varieties (`Sunglo`, `Sunking`, `RedHaven`, `Fair Haven`, and `Hale Berta Giant`) were grafted to rootstockof these seedlings and to the rootstock `Nemaguard` for comparisonpurposes. Fifteen trees of each of the grafted varieties were observedfrom 1986 to 1995 with regard to the following parameters: trunkcross-sectional area, cumulative marketable yield, yield efficiency,blossoming (from 1987 to 1995), tree health, compatibility, frosthardiness, suckering, soil adaptation. Clone 73/95 was one of theseedling clones with the best results.

In 1994, a second trial was performed. Thirty trees from each of fourpeach varieties (`Suncrest`, `Early Red Haven`, `Hale Berta Giant`, and`Redcal`) and seventeen trees from each of three apricot varieties(`Orangered`, `Hargrand`, and `Harlayne`) were grafted to rootstock fromselected Prunus pumila seedlings from the first evaluation and to`Nemaguard` rootstock for comparison purposes. Clone 73/95 displayed thebest results of the seedlings tested and was renamed `Rhenus 2`.

`Rhenus 2` has not been observed under all possible environmentalconditions and its phenotype may vary significantly with variations inenvironment such as temperature, light intensity, and daylength, withoutany variation in genotype. Howerver, the following unique combination ofcharacteristics have been repeatedly observed in asexually propagatedprogeny of `Rhenus 2` and distinguish it from all other varieties: (1)causes substantial dwarfing when used as a rootstock for peach,nectarine, and apricot scions with no significant reduction in fruitsize; (2) compatibility as a rootstock with a wide variety of peach,nectarine, and apricot varieties; (3) when used as a rootstock, providesan early yield, high yield efficiency, substantially uniform fruit size,high frost hardiness, no suckering, and good soil adaptation. Thesecharacteristics are established and transmitted through succeedingasexual propagations.

Asexual reproduction of `Rhenus 2` was performed by hardwood cuttings,softwood cuttings (e.g., tips and intermediate cuttings), stool bedpropagation (layering), and tissue culture. Asexual propagation has beenaccomplished in McMinnville, Oreg. and elsewhere in Germany. Otherconventional methods for propagation of Prunus pumila varieties may alsobe used. Best results have been observed with hardwood cuttings (quickdipping using 4000 ppm indole-3-butyric acid [IBA]).

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are photographs of `Rhenus 2` taken at theResearch Station of Viticulture and Horticulture in Geisenheim, Germany,in September 1995.

FIG. 1 is a view of a typical twig and leaves of `Rhenus 2`.

FIG. 2 is a view of two-year-old nongrafted specimens of `Rhenus 2`.

FIG. 3 is a view of five-year-old `Red Haven` trees grown on `Nemaguard`rootstock (left) and `Rhenus 2` rootstock (right).

DETAILED DESCRIPTION

The following is a detailed description of the invention based on plantsgrown at the Research Station of Viticulture and Horticulture inGeisenheim, Hessen, Germany. Color descriptions and other terminologyare used herein in accordance with ordinary dictionary significance oras commonly used by those of ordinary skill in the relevant art, unlessotherwise noted with reference to The Royal Horticultural Society ColourChart (R.H.S.). It should be noted that color will vary with time ofyear, lighting and growing conditions. For example, leaves tend to bebrighter green if grown in soil with a high nitrogen content and moreyellow if grown in soil with lower nitrogen content.

All `Rhenus 2` trees, insofar as I have been able to observe them, havebeen identical in all the characteristics described below.

Propagation: Holds to distinguishing characteristics through succeedingpropagation by rooted cuttings.

Tree:

Trunk.--Size: FIG. 2 provides a view of typical two-year-old nongraftedspecimens. FIG. 3 provides a view of five-year-old `Red Haven` treesgrown on `Rhenus 2` rootstock (right) and, for comparison purposes, on`Nemaguard` rootstock (left). The trunk caliper on two year old treegrowing in Dundee, Oreg., was one-eighth inch measured about one inchabove the ground. Surface texture: Smooth. Bark color: Bright gray-brown(like R.H.S. 178C on one year old trunk and R.H.S. 177A on two year oldtrunk, growing in Dundee, Oreg.).

Form.--Spread upright, later semi-erect.

Branches.--Surface texture: Smooth. Bark color: Red-brown. New growthcolor: Bright green. Mature growth color: Red-brown. Like R.H.S. 175A onmature one year branches. Mature one year branches are those that havematured over the summer of a single growing season. Internode length:15-20 mm. Lenticels: Yellow-white, pointed-rounded (like R.H.S. 163C).Bud: Color observed in spring in Dundee, Oreg., was brown, like R.H.S.177B.

Leaves.--(see FIG. 1). Size: Generally small. Length averages 70-80 mm,including the petiole. Width averages 20-25 mm. Surface texture: Normalfor the species. Form: Linear elongated. Color: Upper surface is brightto dark green (Like R.H.S. 137D when observed in Dundee, Oreg. in thespring). Lower surface is bright gray-green (Like R.H.S. 139C whenobserved in Dundee, Oreg. in the spring). Mid-vein: Size: average.Color: yellow-green. Petiole: Length normal for species, 10-15 mm.Thickness 0.2-0.3 mm. Color is yellow-green to green (Like R.H.S. 137Dwhen observed in Dundee, Oreg. in the spring). No leaf glands observed.

Flowers.--Size: Small, about 5 mm in diameter. Color: White (Like R.H.S.155C). Number: 2-4 per bud. Fragrance: Very weak. Sexualcharacteristics: Flower is complete, fertile, but self-unfruitful.

Fruit.--No fruit borne by `Rhenus 2` trees in six years of observation.

Soil adaptation and tolerance:

Chlorosis.--No problems observed.

Wet.--No problems observed.

Multiplication ability:

Layering.--Good.

Hardwood cuttings (with IBA).--Very good.

Softwood cuttings (with IBA).--Very good.

Pathogen resistance:

Fungal disease.--No problems observed.

Insects.--No problems observed.

Mites.--No problems observed.

Viruses.--No problems observed. Non-host for plum pox (Sharka)-virus.

Diseases.--No problems observed.

Performance as rootstock when grafted:

Root sprouts (suckering).--None in nine years.

Anchorage.--Very good.

Compatibility.--Very good. No incompatibility observed with any peach ornectarine variety. No incompatibility with apricots after four years'testing. Compatibility expected with most other Prunus species, althoughincompatible with at least some varieties of European plums.

Vigor.--Dwarfing. Prunus tree scions grafted to `Rhenus 2` rootstock areapproximately 70-80% as vigorous as when grafted to `Nemaguard`rootstock.

`Rhenus 2` is useful, for example, as a dwarfing rootsock with peaches,nectarines, and apricots (P. armeniaca), as well as with other Prunusspecies such as plums (e.g., P. domestica, P. salicina). Althoughincompatibility has been observed with some varieties of European plums,`Rhenus 2` is compatible with all varieties of peaches, nectarines, andapricots that have been tested and no graft line problems have beenobserved. For example, the trunk circumference of a `Red Haven` sciongrafted to `Rhenus 2` rootstock is reduced by about 34 percent comparedto a `Red Haven` scion grafted to `Nemaguard` rootstock (155 mm and 235mm, respectively) (Table 1). `Nemaguard` is an unpatented rootstockwhich is commercially available.

Also, the yield efficiency of `Red Haven` peach scions on `Rhenus 2`rootstock is approximately 52 percent higher than `Red Haven` peachscions on `Nemaguard` rootstock (Table 1). Scions grafted to `Rhenus 2`also display early yield or precocity (i.e., a cumulative marketableyield of fruit of a variety grafted to `Rhenus 2` rootstock that issignificantly higher five or six years after planting as compared withthe same scion variety grafted to a reference rootstock).

In general, the yield of a Prunus scion grafted to `Rhenus 2` rootstockis about one year earlier than when grafted to `Nemaguard` rootstock.Moreover, `Rhenus 2` displays high frost hardiness.

In a cold treatment trial, `Rhenus 2` exhibited no observable damagewhen subjected to a temperature of -15° C. for fifteen days, while otherpeach rootstock selections died or were severely injured.

Comparison Tables

The following tables provide data regarding the growth of peachvarieties grafted as scions to `Rhenus 2` and comparisons of the RedHaven peach variety grafted to both `Rhenus 2` and `Nemaguard`rootstock. No significant fruit size differences or graft line problemswere observed. Measurements are made 10-20 cm above the bud union ongrafted trees.

                  TABLE 1                                                         ______________________________________                                        Trunk Circumference and Tree Head Volume of                                   Peach Varieties Grafted to `Rhenus 2` or `Nemaguard`                          Rootstock Five Years After Planting                                                                 Tree Circum-                                                                             Tree Head                                    Variety    Rootstock  ference (mm)                                                                             Volume (m.sup.3)                             ______________________________________                                        Sunglo     Rhenus 2   176        1.2                                          Sunking    Rhenus 2   173        1.2                                          Fairhaven  Rhenus 2   143        1.0                                          Hale Berta Rhenus 2   157        1.2                                          Giant                                                                         Red Haven  Rhenus 2   155        1.2                                          Red Haven  Nemaguard  235        5.3                                          ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Yield Efficiency/Productivity and Fruit Weight                                of Red Haven Grafted to `Rhenus 2` and `Nemaguard` Rootstock                                         Yield     Fruit                                        Variety    Rootstock   Efficiency*                                                                             Weight (g)**                                 ______________________________________                                        Red Haven  Rhenus 2    79         96                                          Red Haven  Nemaguard   52        106                                          ______________________________________                                         *Total yield 1986-1991 (kg) divided by trunk circumference (mm).              **Average of four years.                                                 

I claim:
 1. A new and distinct variety of Prunus pumila plant as hereinshown and described.